Abstract

Related RNA polymerases (RNAPs) carry out gene transcription all three domains of life. This thesis deals with the structure determination of RNAPs and their functional complexes from different species. Protein complexes were preserved in their native state in aqueous solution, imaged by cryo- transmission electron microscopy and structural models were obtained using the single particle reconstruction method. New and physiologically relevant insights into RNAPs subunit architecture, the general transcription mechanism and its regulation were gained.
The structure of an archaeal RNA polymerase identified similarities to its eukaryotic counterpart, RNA polymerase II. The conservation of the overall enzyme architecture as well as the close resemblance of structural elements and functional surfaces needed for basic transcription mechanisms underlines the evolutionary relationship between archaeal and eukaryotic RNAPs.
The comprehensive study of RNA polymerase III and its regulation by Maf1 gave profound insights into the molecular basis of how eukaryotic transcription is shutdown under stress conditions to ensure cell survival. Maf1 binds RNAP III at its clamp domain and rearranges a specific subcomplex needed for interaction with the initiation factor Brf1. This specifically impairs binding of RNAP III to its promoters and inhibits transcription initiation. Furthermore, it was demonstrated that Maf1 binds to RNAP III that is already engaged in transcription elongation, thus leaving activity intact but preventing re-initiation. Taken altogether, these results converge on the essential mechanism of RNAP III-specific transcription repression by Maf1.